This invention relates in general to a system for automatically testing the type of brake system on a trailer employed in tractor/trailer vehicles and upon determination of the type of system with which the trailer is equipped, will properly and automatically connect the vehicle power source to the tractor/trailer. It is generally known that in the mid 1970's anti-lock brakes on heavy tractor/trailer vehicles were mandated under Federal Motor Vehicle Safety Standard 121 and that a few years later the mandate was rescinded by Congress because of the failure rate of the unproven anti-lock brake systems of that day. Since that time, new technology has restored credibility to anti-lock brake systems around the world.
Anti-lock brake systems on tractors typically receive continuous power from a self-contained power supply disposed within the tractor. However, power to operate trailer anti-lock brakes is typically derived from the trailer brake light circuit which is powered through a cord/connector system suspended between the tractor and trailer. This cord/connector system generally consists of six or seven individual conductors or lines each one dedicated to a particular circuit function such as turn signal, tail lights, brake lights, and identification marker lights, etc. Power supplied to the trailer anti-lock brake system from the trailer brake light circuit is intermittent being supplied only when the brakes of the tractor are applied. While today's well designed second generation anti-lock brake systems function acceptably with this method of powering on single trailer applications, it is generally agreed among designers and engineers that continuous power to the anti-lock brake system is a better and safer mode of operation especially when operating a double or triple trailer combination. Under continuous power, self-diagnostics can also be performed continuously on the anti-lock brake system thereby enhancing the reliability and safe operation of the overall system. In addition, voltage drop problems associated with multiple trailer configurations are minimized.
Applicant filed pending patent application entitled Anti-Lock Brake Powering System on May 21, 1992, Ser. No. 07/886,252, for an anti-lock brake powering system that will operate in conjunction with the present invention. In Applicant's pending patent application an additional pressure responsive switch is positioned in the relay valve at the rear of the trailer and is disposed in the trailer brake light circuit and is responsive to air pressure in the trailer air brake lines. In addition, a switch means is disposed in the tractor and is connected to the trailer brake light circuit so that when the switch means is placed in one position the existing electrical brake light circuit in the tractor functions normally to operate the brake lights of a conventional (non-anti-lock brake equipped) trailer from the pressure responsive switch disposed in the tractor. With the switch means placed in a second position, continuous power is supplied to the brake light circuit of a trailer equipped with an anti-lock brake system and the trailer brake lights operate from the pressure responsive switch disposed in the trailer relay valve. Thus, the existing standard seven way cord and plug configuration as is presently employed in most tractors can be utilized to power a trailer equipped with either a conventional brake system or an anti-lock brake system.
Some examples of prior art anti-lock testing and brake powering systems are set forth in patents briefly described below:
U.S. Pat. No. 5,039,173 issued to Emig et al. discloses a system incorporating a separate battery located on the trailer which in combination with the tractor power source provides power to the electronic control unit and solenoids of the anti-lock brake system. This system requires the use of an additional battery which has encountered charging difficulties in actual field use and requires periodic maintenance. Additionally, there is high initial expense to implement such a system.
U.S. Pat. No. 5,085,489 issued to Emig et al. discloses a system which partially powers the electronic control unit of an anti-lock system by utilizing power generated by wheel sensors. Power is supplied only when the wheels of the trailer are moving above a minimum speed and is insufficient to operate solenoid valves in the system. Wheel sensors must be precisely set and are susceptible to mechanical failure.
U.S Pat. No. 3,934,940 issued to Schnalbel discloses a safety interlock circuit for switching brake anti-lock systems in a tractor/trailer vehicle combination in and out. A current sensing device located in the tractor unit senses the differential of current flow into an anti-lock trailer as opposed to a non-anti-lock trailer equipped with a load resistor. Based on this difference, a control circuit enables or disables the tractor anti-lock brake system so as to provide similar braking characteristics for both vehicles. This devise operates in conjunction with a dedicated line that supplies continuous power to the anti-lock trailer such as is common in the European market and is not applicable to trailers in the North American market. This device will enable or disable tractor anti-lock according to the type of trailer connected to it which is not the object of the present invention.
Whatever the precise merits, features and advantages of the aforecited references, none fulfills the purpose of the present invention.
The present invention allows the continued use of the standard six or seven way cord and plug configuration presently used on tractor/trailer combinations while simultaneously providing continuous electrical power to the anti-lock brake system of a trailer.
A further object of the present invention is to automatically test a trailer to determine whether the trailer is equipped with anti-lock or conventional brakes.
Still another object of the present invention is to automatically connect the proper power source to the trailer brake light circuit after automatically testing the trailer for anti-lock or conventional brakes.
Yet another object of the present invention is to enable tractors and trailers equipped with the present invention to interconnect and function normally with conventional tractors and trailers of past and future manufacture.
An additional object of the present invention is to provide for ease of installation and low initial installation and maintenance costs.
A further object of the present invention is to reduce or eliminate the human error factor in properly connecting an anti-lock trailer to the tractor unit equipped with the present invention hence obtaining maximum safety benefits by automatically testing and properly connecting the tractor power source to the anti-lock trailer.
Another object of the present invention is to enhance the overall public safety by enabling the more efficient continuous operation of the anti-lock brake system.
Yet another object is to encourage the skeptical trucking industry to more readily accept anti-lock brake equipped trailers because of a safer mode of operation by virtue of the electronic control unit (ECU) being under continuous power and able to continually self-diagnose itself and display a fault warning light previous to moving the vehicle or depressing the tractor brake pedal.